A typical broadband communication system, such as a coaxial cable communication system (CATV), provides downstream data communications from a centralized node or headend to modems of many users. The downstream data communications are provided from the nodes or headends at specific frequencies. The communication system operators, e.g. multi-service operators (MSOs) may use several data communication frequencies and different frequencies are often used by different operators and different headends. The downstream data frequencies used are typically in a wide frequency spectrum which ranges range from 88 MHz to about 850 MHz.
When a modem is connected to the communications system, it typically scans the downstream frequency spectrum until a data signal is received. The modem typically locks onto the frequency at which the data signal is received. However, the data signal may be received at a frequency which is not the actual transmission frequency from the headend. For example, if an operator transmits a downstream data signal at 150.1 MHz, the modem may start to detect the data signal at 150 MHz and lock onto the 150 MHz frequency, i.e. 1 MHz away from the actual transmission frequency.
A modem maybe preprogrammed with a channel map which instructs the modem which frequencies to scan to detect a downstream signal rather than scanning the entire spectrum. However, an operator may use a transmission frequency which is not on the channel map. Moreover, the lock range, or channel pull up range, of a modem may encompass more than one channel on the channel map. As a result, even with a channel map, the modem may lock onto a frequency which is not the actual transmission frequency.
When a modem locks onto a frequency which is not the actual transmission frequency data will likely be received by the modem but the communications will not be optimal. In some instances, the error rates in the data received, e.g. the packet error rate and/or the bit error rate, may be sufficient to sustain the channel lock but may greatly reduce the communication speed and the quality of the data received. As a result, a user may not receive the data communications speeds from an operator at levels advertised by an operator. A user may also experience frequent loss of data packets which may impair communications with a network element, and may be particularly noticeable in voice communications, e.g. VoIP calls, video applications, and file downloads.